1. Field of the Invention
The present invention relates to a process for producing neopentyl glycol by hydrogenating hydroxypivaldehyde.
Neopentyl glycol is a very important intermediate for industrial use and has a wide variety of applications; for example, it is used in the production of various synthetic resins such as acrylic resins, polyester resins, polyurethane resins, alkyd resins and polycarbonate resins, and also used for a plasticizer, a synthetic lubricating oil, a fiber processing agent and a surfactant.
2. Description of the Related Arts
Neopentyl glycol has been usually produced by the following two processes.
In accordance with one of the processes, isobutyraldehyde and formaldehyde are subjected to an aldol condensation and then to a crossed Cannizzaro reaction in the presence of a strongly alkaline catalyst such as caustic soda, caustic potash, calcium hydroxide or the like to thereby produce the objective neopentyl glycol. This process, however, suffers a disadvantage that since sodium formate is by-produced in an equimolar amount to the objective product when caustic soda is used, the process fails to establish itself as a process for producing neopentyl glycol on a commercial scale insofar as sodium formate thus produced as the by-product can not be effectively utilized.
In accordance with another process, hydroxypivaldehyde as obtained by the reaction of isobutyraldehyde and formaldehyde is hydrogenated in the presence of a catalyst to thereby produce the objective neopentyl glycol, which process is not accompanied with sodium formate as the by-product.
The above-mentioned hydrogenation process is disclosed in Japanese Patent Publication Nos. 33169/1974 and 17568/1978, G.B. Pat. No. 1219162, U.S. Pat. No. 3,920,760, G.B. Pat. No. 1048530, European Patent Nos. 44412 and 44444, U.S. Pat. Nos. 4,855,515 and 4,933,473, etc, in which are disclosed Raney nickel, Ni-Cr, Cu-Zn, Cu-Al, Cu-Cr, Cu-Cr-Ba, Cu-Cr-Mn, Pt-Ru-W, etc. as catalysts for use in the hydrogenation reaction.
As mentioned above, in the process for producing neopentyl glycol by hydrogenating hydroxypivaldehyde, a variety of catalysts have been proposed. However, there still remain the problems in the above known catalysts that the catalytic activity is insufficient and thus the reaction must be carried out under high pressure conditions and that the catalytic activity can not be maintained at a high level for a long period of time since it is decreased under the influences of a slight amount of impurities contained in hydroxypivaldehyde as the starting material, and the like. Further, in the case of Raney nickel catalyst, in addition to the above defects in catalytic activity and persistency thereof, various problems still remain unsolved in that the catalyst can not be easily prepared and handled and that the process inevitably becomes complicated since the catalyst is used in a slurry form.
Moreover, with respect to a catalyst containing chromium, great care must be exercised in the production and handling of the catalyst for industrial use because of the toxicity of chromium. A catalyst containing platinum or ruthenium finds difficulty in the process for the preparation thereof and also in the regeneration thereof at the time of deterioration of the catalytic activity in spite of its using an expensive noble metal, thereby making itself unreasonably expensive. Water is generally used in the above-mentioned hydrogenation process as a solvent, but a low dissolution rate of hydroxypivaldehyde in water causes a troublesome and complicated problem with its dissolution in a industrial process plant.